366 A. \V. GRABAU — SILURO— DEVONIC CONTACT IN NEW YORK 



This species is so closely related to Orthis (Orthothetes) hderstriatus 

 Hall, of the Coralline limestone at Schoharie, thai it is practically im- 

 possible to distinguish the two. In size, outline, and convexity of 

 valves, form, and method of intercalation of striae and character of can- 

 cellating lines, the specimens from the Manlius limestone of Erie county 

 and those of the Coralline limestone of Schoharie county appear to be 

 identical. r l ne only difference observed is in a shallow but broad mesial 

 depression in the pedicle valve which occurs in a number of specimens 

 from Williamsville and Akron, but has not been observed in the Coral- 

 line limestone species ; neither does it always or even very commonly 

 occur in the Manlius limestone species in Erie county, New York. It 

 appears to be characteristic of the specimens of this species from Ohio. 



This species occurs throughout the Manlius limestone in Erie county, 

 but is most abundant in the upper 2 or 3 feet. Sometimes slabs of the 

 stone are covered with the impressions of these shells, one mold oblit- 

 erating the other. Similar conditions occur in this rock at the Ohio 

 localities. 



S PI RIFE R ERIENSIS, SP. NOV. 

 (Plate 21, figures 2o-6.) 



Shell small, pedicle valve strongly convex, almost ventricose, sub- 

 rhomboidal in outline, with the beak much elevated and gently incurved. 

 Mesial sinus pronounced ; angular in the center, with the sides nearly 

 fiat, gradually and uniformly increasing in width from the beak forward. 

 Sometimes it is slightly rounded in the bottom. It is prolonged at the 

 front of the shell as a prominent rounded lip. On either side of the 

 sinus is a moderately strong, broadly rounded, but not very prominent 

 plication, in addition to which there are about three or four on either 

 side, which are fainter and progressively become narrower away from 

 the sinus. Interspaces narrow, having the form of a depressed line, the 

 broadest next to the plication adjoining the sinus. Brachial valve al- 

 most semicircular, moderately convex, with a straight hinge line, which 

 is shorter than the greatest width of the valve. Beak elevated above the 

 hinge line and incurved. Fold distinctly defined by a sharp depressed 

 line on either side, but not elevated much above the general surface of 

 the valve. It gradually and uniformly widens forward, is broadly 

 rounded on top, and is occasionally marked by a slight central depres- 

 sion. Ribs almost obsolete, a faint depression outlining the first on 

 either side of the fold in some specimens. Surfaces of both valves 

 marked by fine, uniform, and subequally spaced concentric lines which 

 curve forward in the sinus of the pedicle valve. Occasionally strong 

 lines mark a temporary resting stage during growth. The whole sur- 



